The present invention relates to a clockspring which electrically connects a stationary housing to a rotatable hub by means of a flat ribbon cable, and in particular to an apparatus which is capable of indicating if the hub is centered with respect to the housing.
Clocksprings are typically used in applications such as connecting an air bag, mounted in the steering wheel of an automobile, to sensors mounted within various locations of the automobile.
For example, U.S. Pat. No. 5,061,195 (1991), issued to Bolen, discloses a type of clockspring providing a direct electrical connection between relatively movable members in the steering apparatus of an automobile. In this type of clockspring construction, a ribbon cable is used to provide the electrical connection. The ribbon cable is constructed of conductive material which is sandwiched between two layers of mylar. The cable is loosely accommodated in a coiled state within the clockspring's housing. In addition, one end of the cable is attached to the clockspring's stationary member and the other end of the cable is attached to the clockspring's rotatable hub.
In operation, the ribbon cable will either wrap or unwrap around the hub when the hub is rotated. However, in order to prevent the cable from being damaged during rotation of the hub, no substantial tensile force is allowed to be applied to the ribbon cable while it is wrapping or unwrapping. An overwound condition is the to occur if the hub is rotated so far in one direction that it results in a significant amount of tensile force being applied to the cable.
In order to prevent excess tensile force from being applied to the cable, it is necessary for the hub to be centered when it is mounted on the steering apparatus. Centering of the hub allows for the same extent of clockwise and counterclockwise rotation of the hub before the ribbon cable becomes overwound.
If the hub is not in the centered position when the clockspring is mounted on the steering apparatus, then the cable will be damaged when it is completely wrapped and/or unwrapped around the hub, but yet the steering apparatus is still allowed to continue to turn.
To ensure that the clockspring is centered when it is mounted on the steering apparatus, external locking mechanisms are sometimes used. These locks allow only limited rotational travel of the hub prior to the clockspring's installation. The external lock is disengaged by simply removing it from the clockspring and discarding it.
Likewise, internal locking mechanism are also sometimes used in order to prevent rotation of the hub such as U.S. Pat. No. 5,171,157 (1992), issued to Bolen. An internal lock limits the travel of the hub whenever the clockspring is not mounted to the steering apparatus. The internal lock is usually disengaged by a pin or other unlocking system provided by the steering apparatus. The clockspring's lock will reengage whenever the clockspring is removed from the steering apparatus.
However, if the hub is removed from the steering apparatus and then subsequently reinstalled, both the external lock and the internal lock fail to ensure and/or indicate when the clockspring's hub is centered.
Many devices have been proposed which provide a way of indicating if the clockspring's hub is centered. However, these devices cause an increase in the diametrical size of the clockspring and/or require the use of gears which have a very limited useful life due to their constant rotating whenever the hub rotates.
For example, U.S. Pat. No. 4,789,342 (1988), issued to Shitanoki, discloses a position indicator which is mounted on the side of the clockspring. Likewise, U.S. Pat. No. 4,821,016 (1989), issued to Zeller et al., discloses an indicator having a plurality of gears which rotate whenever the hub rotates.
Therefore, a centering display device is proposed which has a counter wheel, axially supported on the top of the housing, and a pawl, provided on the hub, which engages the counter wheel when the hub revolves. This device thereby enables centering of the hub and housing members. The device does not, however, increase the diametrical size of the clockspring and/or require the continued engagement of two or more gear members.
In view of the above, it is an object of the present invention to indicate when the hub is centered within the clockspring housing.
A further object of the invention is to provide a centering display without increasing the diametrical size of the clockspring.
An added object of the invention is to provide a centering display device having a high reliability.
Another object of the invention is to indicate the direction that the hub must be rotated in order to position it into a center position within the clockspring housing.
It is also an object of the invention to indicate the number or turns required to position the hub into the centered position.
In addition, it is an object of the invention to reduce or eliminated the possibility of the occurrence of an overwound condition.